docs: def compounds_to_frame(compounds, properties=None):
      """Construct a pandas :class:`~pandas.DataFrame` from a list of :class:`~pubchempy.Compound` objects.
  
      Optionally specify a list of the desired :class:`~pubchempy.Compound` properties.
      """
      import pandas as pd
      if isinstance(compounds, Compound):
          compounds = [compounds]
      properties = set(properties) | set(['cid']) if properties else None
      return pd.DataFrame.from_records([c.to_dict(properties) for c in compounds], index='cid')